DIGESTIVE ORGANS. 221 
in the cecilians). Many reptiles also have a sublingual gland on either 
side (fig. 224). In many snakes a pair of the labial glands are greatly 
developed and have migrated into the zygomatic ligament, where they 
have become modified into the well-known poison glands (fig. 215), 
the ducts of which connect with the poison fangs 
(p. 213). In the only known poisonous lizards 
(Heloderma) the sublingual glands furnish the 
poison. Oral glands are poorly developed in 
the sea turtles and the crocodilians. 
Birds lack the labial and internasal glands, 
but they have numerous other glands opening 
separately into the roof of the mouth (fig. 225) 
as well as anterior and posterior sublinguals and 
frequently an ‘angle gland’ at the angle of the 
mouth, which may be the last remnant of the 
labial glands of the other Sauropsida. 
Besides numerous smaller glands (labials, 
buccals, linguals, palatines) imbedded in the 
mucous membrane and opening separately into 
the mammalian mouth, the salivary glands, 
though absent from the cetacea, form a distin- 
guishing feature of the group. These salivary 
glands are usually in the neighborhood of the 
mouth, but one or more of them may be carried 
back into the neck (fig. 226), but in all cases the 
homologies are decided by the openings of the 
Fic. 225.—Palatal sur- 
face of hen, after Heid- 
rich. ch, anterior end of 
choana; gs, openings of 
sphenopterygoid glands; 
in; infundibular opening; 
lp, mp, openings of lat- 
eral and medial palatine 
glands; m, opening of 
gl. maxillaris monosto- 
matica. 
ducts. The salivary glands include the sub- 
maxillary and sublingual of the lower groups, and in addition the 
parotid gland, apparently a development within the class. The sub- 
maxillary normally lies in the lower jaw beneath the mylohyoid 
muscle, and its duct (Wharton’s duct) opens near the lower incisor 
teeth. Near this is frequently a retrolingual gland, its duct open- 
ing near the former. The sublingual gland occurs between the tongue 
and the alveolar margin of the lower jaw and usually empties by 
numerous duct. The parotid gland has its normal position near the 
ear and its ducts (Stenon’s duct) pours the secretion out near the 
molars of the upper jaw. Other oral glands are occasionally present, 
like the molar glands of ungulates and the orbital glands of dogs, 
both of which have ducts leading into the mouth. 
